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REGIONAL WATER BOARD RESPONSE (SWRCB/OCC File A-1846(a) and A-1846(b)) -10- <br /> PETITIONS FOR REVIEW OF Wr �, DISCHARGE REQUIREMENTS J <br /> ORDER NO. R5-2007-0036 (NPDEo NO. CA0079154) AND <br /> TIME SCHEDULE ORDER NO. R5-2007-0037 <br /> CITY OF TRACY, WASTEWATER TREATMENT PLANT <br /> Table 2— Predicted EC Changes as Tracy Discharge Rate Increases <br /> Tracy Discharge Predicted EC Changes Caused by Tracy Discharge <br /> Old River at Tracy BNd Bridge (NS/cm) <br /> -. Discharge Hih Exports Low-Ex orfs <br /> Flow EC <br /> (m d) (NS/cm) August' October' August' October' <br /> 9 1700 +24 +22 +6 +8 <br /> 10.8 1416 +20 +16 +6 +6 <br /> 12 1274 +18 +11 +5 +4 <br /> 14 1092 +14 +4 +4 +2 <br /> 16 956 j +11 -2 +3 1 <br /> ' Assumes ambient EC of 700 pS/cm <br /> ' Assumes ambient EC of 1000 pslcm <br /> Using actual measured ambient EC data, the relative impact of the City of Tracy discharge in <br /> the southern Delta can be evaluated. Figure 1, below, shows actual Old River EC data <br /> measured upstream of the discharge at Union Island and downstream at the Tracy Blvd <br /> Bridge, which is one of the D-1641 salinity compliance locations. DSM2 modeling output was <br /> used to predict-a reasonable worst-case EC increment caused by the Tracy discharge at the <br /> Tracy Blvd Bridge. As shown in Figure 1, the reasonable worst-case Tracy impact is relatively <br /> small compared to other salinity sources in the area. The other sources of salinity are <br /> unknown, but likely include the ambient salinity entering from the San Joaquin River, <br /> agricultural activities in the area, and possibly groundwater accretions. <br />